The current propagation of wireless devices such as smart phones and various applications are causing an increase in data traffic on wireless networks.
In addition, wireless intelligence communication such as communication between individual devices such as smart TVs, refrigerators and the like other than smart phones may too increase traffic in the wireless network to levels that are difficult to handle.
The D2D communication is highlighted as one alternative to process traffic in wireless networks while not burdening an evolved Node B (eNB). The D2D communication can use a frequency band which is not allowed like a WLAN as well as a frequency band which is allowed to perform wireless communication.
The D2D communication in the allowed frequency band can reduce the load on the eNB. This may allow the eNB to efficiently use limited traffic capacities (acceptable traffic capacities) which the eNB can accept.
For example, User Equipments (UEs) within the same cell or adjacent cells may configure a communication link for D2D communication (hereinafter, referred to as a “D2D link”) in a mobile communication system supporting communication in the allowed frequency band. The UEs can directly exchange data through the configured D2D link without depending on the eNB. Through the D2D communication, it is possible to reduce the number of required links as compared to a case using the eNB. The eNB can use the left over links for other purposes due to the decrease in the number of links.
The D2D communication in the non-allowed frequency band may prevent radio resources from being unnecessarily wasted. Further, it may provide an efficient service for traffic locally generated.
The D2D communication requires discovery, pairing, scheduling and the like after synchronization between devices. The discovery corresponds to an operation in which a device identifies adjacent devices through device identification information broadcasted by other adjacent devices. The pairing corresponds to an operation in which a device configures a D2D link with an adjacent device. The scheduling corresponds to an operation in which devices having the configured D2D link receive resources for the D2D communication.
In general, a network supporting Ad-hoc/sensor communication (hereinafter, referred to as an “Ad-hoc/sensor network”) allocates resources by using a contention-based resource accessing scheme. A Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) scheme is an example of the contention-based resource accessing scheme. When the number of UEs is small in the network, the CSMA-CA scheme can transmit/receive data while avoiding collision without separate complicated management by the network.
The Ad-hoc/sensor network has a problem in that a transmission rate become low in a region where the number of users is large. Accordingly, in consideration of a wireless communication environment in which the number of users is expected to increase, an improved scheduling scheme should be provided.
A network supporting the D2D communication (hereinafter, referred to as a “D2D network”) allocates resources by using a “FlashLinQ scheme”.
The FlashLinQ scheme has been designed for the D2D communication. The FlashLinQ scheme defines a slot like a Time Division Multiple Access (TDMA) scheme for efficiency. The FlashLinQ scheme has no master node which manages the resource allocation. Accordingly, the FlashLinQ scheme allocates slot resources by using a round robin scheme.
The FlashLinQ scheme suggests transforming Request To Send (RTS) and Clear To Send (CTS) control signals used in the CSMA-CA scheme and using them for accessing the resources in the TDMA scheme. The FlashLinQ scheme has been made based on Signal to Interference Radio (SIR) measurement using the RTS and CTS in Wi-Fi. The FlashLinQ scheme is implemented to operate based on an Orthogonal Frequency Division Multiplexing (OFDM) scheme in a synchronized network. Accordingly, the FlashLinQ scheme may obtain favorable capability in comparison with conventional Wi-Fi in a particular environment.
The FlashLinQ scheme allocates a priority to each link and measures interference from a higher link and signal power of its own link, so as to calculate the SIR. The FlashLinQ scheme may simultaneously perform transmission when the calculated SIR is higher than a target threshold. The FlashLinQ scheme may simultaneously perform transmission when the SIR is higher than a target threshold in consideration of interference provided to a higher link by its own link.
The FlashLinQ scheme determines resource allocation and priority according to the round robin scheme. For example, one link is selected according to the priority and a next priority link is selected in consideration of interference with the selected link. Accordingly, the number of links to be simultaneously transmitted is secured. The FlashLinQ scheme shuffles the priorities whenever every resource is determined. This makes all D2D links uniformly receive a transmission chance.
The FlashLinQ scheme has difficulty in efficiently allocating resources in comparison with a scheme considering interference information in the network. This is because a transmitted link is changed whenever the priority is changed. That is, the FlashLinQ scheme cannot use channel information measured in consideration of interference from the previous resource for scheduling.
Since the FlashLinQ scheme depends on a control signal transmitted by a higher link, when interference given from its own link to a higher link is calculated, interference given to the higher link by another link other than its own link cannot be recognized. That is, one device has difficulty in recognizing channel information on adjacent devices in the D2D network, so that the device cannot help but allocate resources depending on partial channel information in D2D communication.
When the device can perform scheduling in the D2D network in consideration of channel information of an adjacent device, that is, an adjacent D2D link, it is possible to allocate resources to secure the maximum capacity.